Re: [syzbot] [mm?] WARNING in ep_write_iter

[Zi Yan]

On Sun Aug 16, 2026 at 4:52 PM EDT, Andrew Morton wrote:
> On Sun, 16 Aug 2026 12:25:48 -0700 syzbot <syzbot+805630f1453e490427fa@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
>> Hello,
>> 
>> syzbot found the following issue on:
>> 
>> HEAD commit:    3d6d817622b0 Merge tag 'scsi-fixes' of git://git.kernel.or..
>> git tree:       upstream
>> console output: https://syzkaller.appspot.com/x/log.txt?x=15927479580000
>> kernel config:  https://syzkaller.appspot.com/x/.config?x=a59830cba91a1981
>> dashboard link: https://syzkaller.appspot.com/bug?extid=805630f1453e490427fa
>> compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
>> 
>> Unfortunately, I don't have any reproducer for this issue yet.
>> 
>> Downloadable assets:
>> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-3d6d8176.raw.xz
>> vmlinux: https://storage.googleapis.com/syzbot-assets/d19e0514c02a/vmlinux-3d6d8176.xz
>> kernel image: https://storage.googleapis.com/syzbot-assets/f6da706811f4/bzImage-3d6d8176.xz
>> 
>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>> Reported-by: syzbot+805630f1453e490427fa@xxxxxxxxxxxxxxxxxxxxxxxxx
>> 
>> gadgetfs: bound to dummy_udc driver
>> ------------[ cut here ]------------
>> 1
>> WARNING: mm/page_alloc.c:5280 at __alloc_frozen_pages_noprof+0x2ce/0x380 mm/page_alloc.c:5280, CPU#0: syz.0.0/5319
>
> Thanks.  drivers/usb/gadget is the offender.
>
> Gemini sums it up well.  "ep_write_iter() needs a bounds check prior to
> memory allocation".  https://share.gemini.google/5NzjyttO0ULc
>
> I expect an easy fix would be
>
> --- a/drivers/usb/gadget/legacy/inode.c~a
> +++ a/drivers/usb/gadget/legacy/inode.c
> @@ -666,7 +666,7 @@ ep_write_iter(struct kiocb *iocb, struct
>  		return -EBADMSG;
>  	}
>  
> -	buf = kmalloc(len, GFP_KERNEL);
> +	buf = kmalloc(len, GFP_KERNEL|__GFP_NOWARN);
>  	if (unlikely(!buf)) {
>  		mutex_unlock(&epdata->lock);
>  		return -ENOMEM;
>
> or do what Gemini said.  Me, I'll add some cc's and run away.

Let’s do this instead of suppressing kmalloc WARNs. Since a similar WARN[1]
showed up yesterday and that WARN is better handled by a bound check,
I do not think we want to lose the WARN from kmalloc/the page allocator.

[1] https://lore.kernel.org/all/6a863306.ae6ddae5.3da009.0013.GAE@xxxxxxxxxx/

Like the patch below: